Polymer blends of polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) copolymer have long been known. Because of their particular combination of properties comprising heat-resistance, good (low temperature) toughness and improved processing behavior relative to pure polycarbonate, PC-ABS blends are particularly suitable, for example, for automotive interior and exterior applications.
Flame resistance may be imparted to these blends by halogen-based, but in particular by halogen-free flame retardants. Flame-resistant PC-ABS blends, in particular those based on halogen-free phosphate esters as flame retardant, have become well established in the fields of electrical engineering and information technology over the last 15 years.
To improve the long-term service life of the materials, in particular when used at elevated temperature and ambient humidity, it is desirable to improve the hydrolysis resistance of the materials. Hydrolysis resistance is understood to mean retardation of the degradation of the molecular weight of the polycarbonate.
The use of inorganic calcium carbonates such as described in JP-A 2002-060610 is suitable for this purpose. The compounds described therein are in the particle-size range of 2-5 μm.
On the other hand, a high degree of toughness is demanded of the functional parts produced from the molding compositions.
However, as a rule the addition of inorganic fillers results in an impairment in particular of notch impact resistance.
The object of the present invention was thus to provide PC-ABS compositions which are distinguished by improved hydrolysis resistance while maintaining a high degree of toughness.
It has surprisingly been found that the addition of very finely divided calcium carbonates with an average particle diameter of less than 100 nm greatly increases hydrolysis resistance without impairing the toughness of the blend.